The present invention is concerned with the foaming problem encountered in the paper industry. By way of example, such steps as pulp cooking, the beating of paper stock, closed water circulation in paper machines, dispersing of pigments for paper making, and paper coating all give rise to foaming problems.
Various antifoam agents have been suggested for the paper industry. U.S. Pat. No. 4,950,420 discloses the use of a surfactant polyether together with a fatty ester of a polyhydric alcohol, such as a mono- or diester- of polyethylene glycol. Unfortunately, such polyethylene glycol ester defoamers containing 1,4-dioxane which may present a safety hazard.
Certain prior an patents deal with antifoam agents based on oil-in-water emulsions. For example, EP-A-O 140812 discloses such an oil-in-water emulsion wherein the oil phase contains a C.sub.12 to C.sub.22 alcohol, a fatty ester of a C.sub.12 to C.sub.22 carboxylic acid, and a trihydric C.sub.1 to C.sub.18 alcohol. Similarly, EP-A-O 322830 discloses an oil-in-water emulsion containing its oil phase:
(a) a C.sub.12 or greater alcohol, fatty esters of alcohols of not less than 22 carbon atoms and C.sub.1 to C.sub.36 carboxylic acids and/or; PA1 (b) a fatty ester of a C.sub.12 to C.sub.22 carboxylic acid with a monohydric to trihydric C.sub.1 to C.sub.18 alcohol, together with; PA1 (c) a mixture of polyglycerol esters derived from 15 to 40 wt % diglycerol, 30 to 55 wt % triglycerol and 10 to 25 wt % tetraglycerol. Minor amounts of other polyglycerols may also be esterified. The use of such emulsified multipart systems while effective necessitates several formulation and emulsification steps for product production. Such emulsions typically have limited stability and must be used in a relatively short period of time.
Thus there is a significant need for a single phase, 1,4-dioxane free defoaming agent effective in aqueous paper processing operations.